1. Field of the Invention
This invention relates to a device for adjusting the optical axial position of a lens, and more specifically to a device for adjusting the position of a lens in the optical axial direction thereof when the lens is assembled and adjusted into a complete optical unit.
2. Description of the Prior Art
When the lens or lenses are assembled into an optical unit, the position of a lens mounted in a lens barrel must be adjusted in the optical axial direction thereof, for effecting infinite focus distance adjustment, zooming adjustment, back focus distance adjustment, and the like. The lens barrel normally has a cylindrical stationary member to be coupled to a body of the optical unit, a lens frame supporting member coupled to the stationary member through helicoidal threads, and a lens frame to which a lens is to be mounted and which is coupled to the lens frame supporting member through screw threads.
The most conventional way of adjusting the optical axial position of the lens, is to extend or retract the lens frame axially relative to the lens frame supporting member, whenever the lens frame is rotated with respect to the lens frame supporting member.
In the above-mentioned method, it is possible to adjust the axial position of the lens continuously or steplessly relative to the lens frame supporting member by adjusting the amount of the thread engagement between the lens frame and the lens frame supporting member. After being adjusted, the lens position must be locked by means of an appropriate locking mechanism.
Conventionally, various lens frame locking mechanisms have so far been adopted as follows:
In a first example, a lens is mounted on a lens frame, the lens frame is engaged via screw threads with a lens frame supporting member (e.g., focusing ring), and the lens frame supporting member is coupled to a stationary member through helicoidal threads. After the lens frame has been adjusted relative to the lens frame supporting member by adjusting the amount of the thread engagement between the lens frame and the lens frame supporting member, a spacer washer having a selected thickness is sandwiched between a flange of the lens frame supporting member and a flange of the lens frame. Thereafter the lens frame is tightly screwed against the lens frame supporting member to lock the lens frame to the lens frame supporting member.
In this first example, however, there exist problems which result from the fact that the thickness of the spacer washer must be carefully selected and the lens frame must be removed from the lens frame supporting member before sandwiching the selected spacer washer between those two parts.
In a second example, after the lens frame has been adjusted relative to the lens frame supporting member in such a manner as stated above, the lens frame is locked by use of an additional locking unit. The additional looking unit is a locking nut which is to be screwed to an inner thread formed in the lens frame supporting member, whereby the rotational movement of the lens frame with respect to the lens frame support member is restricted by fastening the locking nut against the lens frame.
In this second method, however, there exist other problems. Namely, a special jig is required to screw the locking nut. As a result, the lens frame is likely to be dislocated or the lens is likely to be scratched when the locking nut is fastened too tightly toward the lens frame.
In a third example, after the lens frame has been adjusted relative to the lens frame supporting member, the lens frame is fixed to the lens frame supporting member by screwing a set screw or set screws from the outer circumferential surface of the lens frame supporting member to the lens frame in the radial direction of the lens.
Again, problems exist as a result of using the third method. Namely, the lens frame or the lens frame supporting member is likely to be deformed when the set screws are fastened too tightly.